1. Field of the Invention
The present invention relates to an apparatus for shaping a row of helically coiled slide fastener coupling elements containing a core thread extending through a longitudinal space defined in the coupling elements.
2. Prior Art
Japanese Patent Publication No. 46-1132 published on Jan. 12, 1971 and U.S. Pat. No. 4,002,278 issued on Jan. 11, 1977 disclose methods of and apparatus for shaping a filamentary material into a row of helically coiled coupling elements in which a core thread is supplied to a shaping position at a rate greater than the rate at which the coupling elements are formed, or it is fed positively to the shaping position while it is protected from being subjected to an excess back tension or reversely directed force, whereby the core thread as received in the coiled coupling elements becomes slightly slackened between adjacent ones of the coupling elements for cancelling out its shrinkage when the coupling elements are sewn to a slide fastener stringer tape. According to such known methods and apparatus, however, the core thread is not stretchable enough to cancel or taken out such shrinkage. The coupling elements containing such core thread can not be secured to the tape stably in position and is likely to become wavy. Further, the prior methods and apparatus have been found insufficient to control a degree of stretchability of the core thread as received in the coupling elements and maintain such stretchability at a constant rate throughout the length of the core thread.